tests/glibmm_tls_client: Catch exceptions from more function calls
tests/glibmm_tls_client: Catch exceptions from more function calls

Gio::Socket::create() can throw an exception. Put it in a try block.
See #84

GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm